The abnormal accumulation of -amyloid (A) in the brain is believed to play a pivotal role in the etiology and pathogenesis of Alzheimer's disease (AD). A is produced continuously in the brain, but under normal circumstances its accumulation is prevented by its rapid catabolism. Compared to the breadth of knowledge concerning the enzymes and pathways involved in A production, relatively little research has been devoted to understanding A removal. Two lines of evidence indicate that endothelin-converting enzyme (ECE)-2 is an A degrading enzyme that regulates steady-state levels of the peptide in the brain, and that alterations in its activity potentially contribute to AD pathogenesis. First, we have shown that the steady-state levels of endogenous A are increased in the brains of mice deficient in ECE-2, similar to that observed in animals transgenic for AD-causing presenilin mutations. Second, ECE2 has been shown to be the single most down- regulated gene in AD brain by microarray analysis. Based on these data, our working hypothesis is that alterations in ECE-2 activity influence AD pathogenesis. We will test this hypothesis in three interrelated Aims that examine the ability of ECE-2 to directly degrade A in vitro and promote alterations in pathology in vivo in animal models. In addition, we will examine ECE-2 expression in our large series of brain tissue from autopsy- confirmed AD cases and age-matched controls and identify and analyze genetic variants in ECE2 to determine whether these correlate with alterations in gene expression and susceptibility to late-onset AD (LOAD). PUBLIC HEALTH RELEVANCE: Alzheimer's disease is the most prevalent cause of dementia in the elderly, currently affecting over 5 million Americans. Many scientists believe that AD is caused by the abnormal accumulation in the brain of a small peptide called A. We have discovered an enzyme that can eliminate this peptide from the brain, and in this application we will further characterize how this enzyme functions, and determine whether differences in its concentration affect one's risk of developing AD. Understanding the role of this enzyme in AD may lead to the development of new diagnostic tests and potential therapeutics.